Author: Andrew Darby
Source: The Age
Date: 28 March 2013
Scientists have pulled off a daring close encounter with Earth’s biggest animal, the Antarctic blue whale, using world-first acoustic tracking techniques.
An Australian-led international team for the first time homed in on the marine giants from hundreds of kilometres away by listening for their songs.
Then, in a hazardous operation in icy waters, a small boat team sped within metres of the fast-moving mammals, which can weight up to 100 tonnes, to dart some for scientific data.
Getting up close to a 30 metre blue was “pretty mind-blowing”, said Virginia Andrews-Goff, whose job it was to fire the darts.
“Certainly I was the size of an ant in comparison.”
Dr Andrews-Goff said she was able to fire satellite tags into two blues’ blubber layers, and watch over the next two weeks as one swam 2000 kilometres, confirming the species’ great range through the Southern Ocean.
Others were sampled with biopsy darts that will yield evidence of the whales’ food, as well as tell whether human pollutants are accumulating in their bodies.
The project underscored the strength of non-lethal techniques, according to Australian Antarctic Division chief scientist, Nick Gales.
“There simply isn’t a scientific reason to go and kill a whale in the Southern Ocean,” Dr Gales said.
Its key was the use of sonar listening devices developed from anti-submarine warfare to find what acoustician Brian Miller said was the equivalent of a needle in a haystack.
Commercial whaling last century killed around 340,000 Antarctic blues, reducing their estimated population to a few hundred by the 1970s.
Today, perhaps a couple of thousand of the endangered animals now roam the ocean, Dr Miller said.
Until now, scientists have studied the whales by following migratory routes, in the hope of encountering blues along the way.
Instead, using sonar to listen for their extremely low-pitched 20-30 second song, Dr Miller said it was possible to hear a blue singing from up to 1100 kilometres away, and gradually home in on the song.
“It’s a very deep song, but all of the Antarctic blues sing the same tune,” Dr Miller said. “They have perfect pitch.”
The research team left New Zealand in January on the chartered fishing boat Amaltal Explorer to work in waters from the Ross Sea region to far south of Tasmania, and analysed 26,545 blues calls on the voyage.
As the ship approached singing whales, Dr Miller’s team was able to triangulate their positions within a few kilometres by dropping sonobuoys into the icy waters.
Observers aboard the Amaltal Explorer were able to do the rest, directing the ship close enough for photo-identification of the whales, or for the darting crew to be launched.
A total of 57 photo-identifications were collected. Dr Andrews-Goff said that by examining dorsal fin shape and skin mottling patterns, scientists could catalogue individuals and compare sightings in later years.
Already one blue with a distinctive fin shape found on this voyage was found to have been photographed off the French Dumont d’Urville base in 2006, she said.
She predicted the voyage’s results would change the way whale research was conducted.
“This method of studying Antarctic blue whales has been so successful it will now become the blueprint for other whale researchers across the world,” Dr Andrews-Goff said.